This invention relates to glass compositions having improved refining and/or melting characteristics. In a conventional float line process, glass batch materials are heated in a furnace or melter to form a glass melt. The glass melt is poured onto a bath of molten tin (tin bath), where the glass melt is formed and continuously cooled to form a float glass ribbon. The float glass ribbon is cooled and cut to form solid glass articles, such as flat glass sheets. For float glass, the glass batch often includes soda, line and silica to form soda-lime-silica based flat glass.
Glass composition properties can be defined based on their temperature and viscosity characteristics. For example, the melting temperature of a glass is often defined as the temperature at which the glass has a viscosity of 100 poises, which is often referred to as the temperature of the log 2 viscosity.
There is a tradeoff between glass production and the cost of manufacture. In particular, it is desirable to increase the rate of glass production but at the same time it is also desirable to reduce production costs. Certain glass manufacturers are operating their glass furnaces at higher and higher throughput and temperatures to meet the increased demand for glass. However, as more glass batch is processed, more fuel is required to melt the increased amounts of glass batch thereby increasing production costs and decreasing thermal efficiency.
Certain prior art has attempted to solve these problems. For example, U.S. Pat. No. 6,797,658 (the disclosure of which is hereby incorporated herein byh reference) discloses decreasing the amount of MgO in the glass composition and increasing the amount of two or more of CaO, R2O (Na2O and K2O), Al2O3, and SiO2 by the same amount. The '658 Patent contends that the melting and/or forming temperature of the glass can be reduced in such a manner. See also U.S. Pat. Nos. 6,878,652 (decreasing MgO and increasing CaO by the same amount), and 5,071,796, the disclosures or which are hereby incorporated herein by reference. However, these compositions are problematic for numerous reasons and do not provide for the best results.
In view of the above, it will be apparent that there exists a need in the art for a soda-lime-silica based glass composition which may realize a lower melting point and/or lower temperature(s) of forming, and/or a lower liquidus temperature. In certain example instances it would be desirable to provide a glass composition that is able to realize a lower viscosity at high temperatures so that refining of the melt occurs faster in the float line manufacturing process, and./or a method of making such glass.